This invention relates to the regeneration of molten zinc chloride catalyst used in the hydrocracking of coaly solids and products derived from coaly solids such as coal extracts or coal liquefaction products.
A process for utilizing molten zinc chloride in such catalytic hydrocracking is described in British Pat. No. 1,095,851. As set forth in that patent, it was found that polynuclear hydrocarbons, even those which are non-distillable, may be readily converted in the presence of a large quantity of molten zinc chloride to low boiling liquids suitable for fuels, such as gasoline. The amount of zinc chloride which serves as catalyst is at least 15 weight percent of the inventory of hydrocarbonaceous material in the hydrocracking zone. To this amount of zinc chloride is added, in the case of nitrogen- and sulfur-containing feedstock, sufficient zinc chloride to remove reactive nitrogen and sulfur compounds in the feedstock, in accordance with the following equations: EQU (1) ZnCl.sub.2 + H.sub.2 S = ZnS + HCl EQU (2) ZnCl.sub.2 + NH.sub.3 = ZnCl.sub.2 .multidot.NH.sub.3 EQU (3) znCl.sub.2 .multidot.NH.sub.3 + HCl = ZnCl.sub.2 .multidot.NH.sub.4 Cl
In the case of a feedstock consisting of coal extract containing, for example, 1.5 percent N and 2 percent S, the amount of zinc chloride required to react stoichiometrically with the nitrogen and sulfur compounds would be 23 percent by weight of the feedstock.
The spent zinc chloride melt from the hydrocracking zone contains (in addition to zinc chloride) zinc sulfide (see Equation 1), ZnCl.sub.2 .multidot.NH.sub.3 (see Equation 2), organic residue, and ash, as well as zinc oxide if the latter were used as an HCl acceptor. U.S. Pat. No. 3,355,376 describes two methods of regenerating the spent zinc chloride melt, both involving oxidation of the impurities, one in liquid phase and one in vapor phase. The reactions occurring in such oxidative regenerative processes are set forth in the following equations: EQU (4) NH.sub.3 + 3/4 O.sub.2 = 1/2 N.sub.2 + 3/2 H.sub.2 O EQU (5) znO + 2 HCl = ZnCl.sub.2 + H.sub.2 O EQU (6) znS + 3/2 O.sub.2 = ZnO + SO.sub.2 EQU (7) c + o.sub.2 = co.sub.2 EQU (8) c + 1/2 o.sub.2 = co
in vapor phase oxidation, air is used to effect combustion of the organic residue, to thereby establish and maintain a temperature in the regenerator at which zinc chloride is vaporized. The effluent zinc chloride vapors carry with them finely divided solids containing zinc values in the form of water-soluble and water-insoluble compounds, for example, "free" zinc oxide and zinc oxide chemically combined with acidic oxides such as silica which are present in the feedstocks to the hydrocracking zone.
In the above-cited related application, Ser. No. 764,616, a process is described for recovery of zinc values which are entrained in the effluent zinc chloride vapors from a vapor phase oxidative regenerator. The regenerative process therein described comprises four steps. In the first step, the spent zinc chloride melt from the hydrocracking zone is subjected to vapor phase oxidative treatment by combustion of the carbon and sulfur compounds, as well as any ammonia that may be present. In this step, the temperature is maintained at least high enough to assure vaporization of the zinc chloride. The effluent vapors contain finely divided solids composed of zinc oxide and zinc oxide complexes derived from the feedstock to the hydrocracking zone, some of which we now known to be water-soluble, and some water-insoluble, e.g., ZnO.multidot.SiO.sub.2. There generally is some residual organic residue in the entrained solids. The second step of the process consists of the separation of the zinc chloride vapors from the solids by any conventional means, generally a cyclone. The third step consists of the treatment of the separated solids with a hydrogen chloride-containing gas under conditions favoring the reaction of zinc oxide and hydrogen chloride at a temperature sufficiently high to form zinc chloride in the vapor state. In the fourth step, vaporous zinc chloride is separated from the ash and condensed to the molten state for recycle to the hydrocracking zone.
The primary object of the present invention is to provide an improvement in the process for regenerating spent zinc chloride whereby the rate of recovery of zinc values from the solids entrained in the effluent zinc chloride vapors from the regenerator is increased.
The following patents were considered in the preparation of this application: Br. Patent No. 1,095,851, U.S. Pat. Nos. 3,355,376, 3,371,049, 3,594,329, 3,625,861, 3,629,159.